1. Field of the Invention L This invention relates to an automatic transmission designed to selectively establish a plurality of gear shift stages by fixing gears to a rotary shaft through frictionally engaging elements, and, more particularly, to a three-shaft type automatic transmission including a sub-shaft in addition to an input shaft and an output shaft.
2. Description of the Prior Art
There are conventionally known three-shaft type automatic transmission such as described in Japanese Patent Application Laid-open No. 175844/85.
Such conventional three-shaft type automatic transmission includes an output shaft and a sub-shaft disposed in parallel on opposite sides of a central input shaft connected to an engine through a torque converter and is designed, so that any of first to fifth gear shift stages may be selectively established between the input shaft and the output shaft by means of two frictionally engaging elements mounted on the input shaft, two frictionally engaging elements mounted on the sub-shaft and one frictionally engaging element mounted on the output shaft.
In such three-shaft type automatic transmission, however, the sub-shaft, having the two frictionally engaging elements, and the output shaft, having the one frictionally engaging element, are disposed on opposite sides of the central input shaft having two frictionally engaging elements. Therefore, the frictionally engaging elements, each having a relatively large size, are laid out unsymmetrically with respect to the central input shaft. For this reason, the internal space in the transmission case is not effectively utilized. Hence, it is difficult to reduce the size of the transmission case. Another problem is that it is impossible to freely change the positional relationship among the input shaft, the output shaft and the sub-shaft, thereby impairing the degree of freedom of layout when these shafts are mounted in a vehicle, and impairing a property for general purpose.